The objective of the proposed studies is to increase our knowledge of the role which noradrenergic neurons originating in the nucleus locus coeruleus (L.C.) have in regulating physiological and behavioral processes in primates. Methods have been developed for locating, stimulating, and lesioning the L.C. in the stumptail monkey (Macaca arctoides). The nature of the behavioral changes produced by manipulations of the L.C. in individual and social situations has led us to hypothesize that there is an integral relationship between the function of the L.C. and anxiety or fearfulness. Physiological and behavioral experiments are proposed by which this hypothesis may be accepted, modified, or rejected. In addition, experiments are proposed which will allow us more specifically to relate manipulation of the L.C. and its projections to behavioral and physiological processes. It is anticipated that such information may lead to an increase in our understanding of the biological basis of mental illnesses which have been associated with possible disorders of noradrenergic function.